Sound reproducer



April 1930. E. FREUND 1,752,981

SOUND REPRODUGER Filed April 12, 1929 ATTORN Patented Apr. 1, 1930UNITED STATES EDWARD FREUND, OF LONG BEACH, NEW YORK SOUIN D REPRODUCERApplication filed April 12,

My invention relates to the class of sound reproducer employed as a loudspeaker for radio receiving'sets, and also as the sound reproducer forphonographs operating with electric reproducers or pick-ups.

The object of my invention is to improve the type of loud speakerwherein a woven fabric is utilized as the vibrating body or diaphragmfor reproducing the sound, and especially the type of speaker whereintwo such diaphragms are drawn together at the center and at which pointthe connecting link from the armature of the electro-magnetic speakerunit is attached; and more particularly my 16 invention relates to themethod of stretching the fabric diaphragms.

In carrying my invention into effect I provide two fabric diaphragmsmade from sheets, preferably one larger than the other,

20 joined at the center, and stretched between suitable frames which areheld rigidly spaced so as to form two cones, one of greater depth thanthe other, and an electro-magnetic vibrator which is connected to thediaphragms at the apexes of the two cones where they are joinedtogether. I also provide means for adjusting the tension of thediaphragms, such means being preferably the same .means whereby the coneframes are held together.

In carrying out my method of connecting and stretching the diaphragms toform cones,

I employ two frames which are connected to gether by means of tensionadjusting means' The fabric sheets are first secured together at thecenter by perforating the sheets and then binding them together by meansof a tubular bolt and clamping washers, or other suitable device, whichalso serves as the means for attaching the vibrator to the cones. Thenthe smaller of the twosheets is stretched upon one of the frames, carebeing taken to stretch the fabric uniformly in all directions andwithout a wrinkle so as to be perfectly fiat. The larger sheet is thendrawn over the other frame, care also being taken to draw it uniformly,and in stretching same it is taken up step-by-step around the frameuntil drawn as taut as possible by hand and without wrinkles. Since thesmaller sheet was drawn flat and taut'while the larger sheet-hung loose,it

1929. Serial No. 354,537.

will be seen that the larger sheet will immediately-assume a cone shapewhen it is attached to its frame, and that the pull in drawing it tautwill create a pull at the center of the smaller sheet and draw it intocone shape. as The cone of the smaller sheet, however, will, due to itshaving been first drawn taut and flat, be quite shallow compared to thecone produced by the larger sheet. The stretching so far is all done byhand,and when the large sheet is fully stretched to the limit by hand, afinal stretching is imparted to both cones by adjusting the braces orstruts by which the two frames are secured together.

In the accompanying drawing which illuso5 trates my invention, Figure 1is 'a perspective schematic view illustrating a pair of coneshapeddiaphragms mounted between a pair of frames adjustably held together;Figure 2 a plan view of the fabric diaphragms be fore being securedtogether and before mounting on the frames; Figure 3 an enlarged centralcross section illustrating the clamping joint for the fabric sheets andspeakor link; Figure 4 an enlarged vertical section showing one of theadjustable struts for the diaphragm frames; Figure 5 a perspectiveschematic View illustrating the first step in stretching the fabricdiaphragms on the frames; Figure 6 a central vertical cross sectionshowing the first stretching of the larger fabric sheet; and Figure 7 anend elevation i1- lust'rating the finished state of the device.

' Referring to the drawings, 1 and 2 indicate rectangular wooden frames,but it will as be understood that these frames may be of any othermaterial. The shape of the frame is more important and I employ angularframes in preference to circular frames. 3 and 4.- are the small andlarge fabric sheets, respectively, as shown in Figure 2, and thesesheets are secured together at the center as shown at 5. The sheets forthis purpose are perforated and the manner of securing them together isshown in Figure 3. The device 6 for securing the sheets together is madelike a pin-vise having a shouldered part 7 and a screw-threaded tubularshank 8. The fabric sheets 3 and 4 are placed between washers 9 and 10and the shank 8 is passed through 10o the electro-magnetic vibrator andis inserted in pin-vise 6 when the vibrator is placed in position.

The electro-magnetic vibrator may be of any desired type or constructionand is only conventionally shown in Figures 1 and 7 by its cover orcasing 13. The vibrator is preferably mounted on frame 1, or on supports14 secured thereto, so that the vibrator will be adjacent the shallowcone 3 and hence the rod 12 connecting the vibrator with the cones willbe relatively short.

The diaphragm frames 1 and 2 are secured together by four screw-threadedrods 15 which pass through holes in the frames.

28 Frame 2 is locked in position on rods 15 by nuts 16 and 17, and framel is adjustahly held on rods 15 by nuts 18 and wing-nuts 19 as shown indetail in Figure 4. To increase the tension of the fabric cones, nuts 18are retracted and then wing-nuts 19 are each screwed up against theframe, step-by-step to insure even pull on the diaphragms, and when thedesired tension is obtained, nuts 18 are screwed down against the frameto lock it in position.

The fabric sheets are secured to the frames by pins or nails 20. Thesepins are driven through strips 21 which are secured to the frames 1 and2 with the pin points projecting outward as shown in Figure 4. Thefabric sheets of Figure 2 are then placed on the frames as shown inFigure 5, the larger sheet 4 hanging loosely, and sheet 3 being held byfour pins at diametrically opposite points 22 4 (which are marked onthesheets when arranging them for punching the central hole 5) to insurecentering the pin-vise 6 within the frames. Sheet 3 is then hooked overthe other pins of frame 1. The sheet is then drawn taut by lifting itfrom one or more adjacent pins, giving a little more stretch to thesheet and rehooking it. This operation is repeated around the entireframe until the desired tension is obtained, and when evenly drawnwithout wrinkles, pins 21 are bent over as shown in Figure 1, thesurplus fabric is trimmed away, and finishing strips of wood 23, Figure7, are applied to cover the edge of the fabric and the bent over pins.In the operation of drawing the sheet taut I find that the bestv resultsare obtained by first slightly taking up the sheet on a few pins next toand on one side of a central point 22, then similarly taking up thesheet at the other side of the same central point.' Then I repeat thisoperation at the opposite side of the frame, and then on the other twosides of the frame. After that is done I begin taking up again whereIleft olf, say at the right of the first point 22, and work graduallytoward the 'corner of the frame, and repeat this operation at the leftof that point 22. This operation is repeated on the opposite side of theframe and likewise on the other two sides of the frame. By this methodthe material is drawn evenly toward the corners of the frame and therebyavoiding the formation of wrinkles in the cloth. Sheet 3 will at thisstage be drawn flat across frame 1. Sheet 4 is now adjusted to frame 2in a similar manner. First, the sheet is grasped at opposite points 22on either parallel sides and is drawn as taut as possible and hookedover opposite centrally located pins 21 on frame 2; then, sheet 4 isgrasped at diagonally opposite points, 22, stretched taut and similarlyhooked over centrally located pins. The sheet being now hooked over theframe 2 at four diametrically opposite points 22 is then hookedsuccessively over the other pins on frame 2 and drawn evenly in themanner above described in connection with sheet 3. In this operationsheet 4 is drawn into a cone shape and gradually more stretch is givento the fabric in the same manner as sheet 3 was drawn taut until sheet 4is drawn as evenly, without wrinkles, and as tightly as possible byhand. The fabric is then trimmed and pins 21 bent over, and strips 23are applied to cover the edge of the fabric and the bent over pins.

In attaching sheet 4 to its frame and gradually drawing it up, acorresponding pull will be imparted to sheet 3, which thus becomesslightly dished as shown in Figure 6, and as sheet 4 is drawn up furtherover frame 2, the cone shape of sheet 4 gradually becomes shallower andthat of sheet 3 deeper until approximately the relatix e proportions ofFigure 7 are obtained. A final stretch is imparted simultaneously toboth cones by means of the adjustable struts or braces 15 as aboveexplained.

The fabric which I prefer to employ for diaphragms 3 and 4 is what isknown as airplane cloth and after the cloth is fully stretched on theframes, either before or after facing strips 23 are applied, I coat thefabric with the waterproofing solution-usually employed onairplanewings. This solution in drylng draws the fabric more taut and1mparts a membranous appearance thereto.

After the water proofing coating on the.

fabric is sufiiciently dry, the electro-magnetic unit is mounted inposition, and the vibrator rod 12 is inserted in pin-vise 6 and thecollar screwed down to cause the vise jaws to firmly grip the rod. Thesound reproducer may now be completed by applying a suitable ornamentalcovering around the frames to enclose the cones 3 and 4 and agrille ormeshcovering may be applied over frame 2 to conceal the interior of cone4, or the device may be enclosed in aspeaker cabinet as is commonpractice. Such covering or cabinet arrangements being well known andforming no part of my present invention are for simplicity ofillustration omitted from the drawing.

I am aware that two fabric diaphragms have been employed as the resonantbody in so-called loud speakers, and my invention is designed to improveupon the construction and resonant quality of this type of soundreproducer. The resonant quality of the fabric diaphragms is improved bydrawing them evenly in the manner above described whereby a cone shapeis imparted to both diaphragms from apex to frame, as distinguished frommerely drawing conical depressions at the centers of the diaphragms. Inother words the maximum conical area is obtained and by arranging thefabric sheets so as to procure a shallow cone and a very deep cone, therange of frequencies to which the sound reproducer will respond is verymatcrially increased, the over and under tones are more clearly broughtout, and the quality and characteristics of the sounds are moreaccurately reproduced.

lVhat I claim is:

.1. A sound reproducer having in combination, a pair of cone-shapedfabric diaphragms, said diaphragms being joined together at the apexesof the cones, two frames between which said cones are held taut, andstruts between said frames for securing sam in spaced relation.

2. A sound reproducer having in combination, a pair of cone-shapedfabric diaphragms, one of greater depth than the other, and saiddiaphragms being joined together at the apexes of the cones, two framesbetween which said cones are held taut, and struts between said framesfor securing same in spaced relation.

3. A sound reproducer having in combination, a pair of cone-shapedfabric diaphragms, said diaphragms being joined together at the apexesof the cones, two frames between which said cones are held taut, andadjustable struts between said frames for securing same in spacedrelation and for adjusting the tension of said cones.

4. A sound reproducer having in combination, a pair of cone-shapedfabric diaphragms, one of greater depth than the other, and saiddiaphragms being joined together at the apexes of the cones, two framesbetween which said cones are held taut, and adjustable struts betweensaid frames for securing same in spaced relation and for adjusting thetension of said cones.

5. A sound reproducer having in combination, a pair of fabric diaphragmsjoined together at their centers, two frames between which saiddiaphragms are drawn into cone shape, the conical surfaces extendingfrom apexes to frames, and struts between said frames for securing samein spaced relation.

6. A sound reproducer having in combination, a pair of fabric diaphragmsjoined together at their centers, two frames between which saiddiaphragms are drawn into cone shape, the conical surfaces extendingfrom apexes to frames, and one of said cones being 8. A sound reproducerhaving in combination, a pair of cone-shaped fabric diaphragms, a pairof stretching frames, a plurality of adjustable struts between saidframes for securing the frames together in spaced relation and forstretching the diaphragms, and a connecting means securing the apexes ofsaid cones together and for attachment to an electric speaker unit.

9. A sound reproducer having in combination, a pair of cone-shapedfabric diaphragms, one of said cones being of greater depth'than theother, a pair of stretching frames, a plurality of adjustable strutsbetween said frames for securing the frames together in spaced relationand for stretching the diaphragms, and a connecting means for securingthe apexes of said cones together and for attachment to an electricspeaker unit.

10. A sound reproducer having in combi nation, a pair of fabricdiaphragms joined together at their centers, a pair of frames betweenwhiph said diaphragms are drawn into cone shape, the area of'the conebases bein the same and the conical surfaces extending from apexes toframes, and one of said cones being of greater depth than the other, aplurality of -adj ble struts between said frames for securing the' fframes together in spaced relation and for stretching the diaphragms,and a connecting means for securing the apexes of said cones togetherand for attachment to an electric speaker unit.

11. The method of producing sound reproducer cones, consisting insecuring tw fabric sheets together at the centers of th sheets,stretching same between two spaced frames by first securing andstretching one sheet taut and flat while the other remains loose, thenstretching and securing the sec- 0nd sheet and gradually increasing theteniso sion thereby drawing the first sheet into a shallow cone.

12, The method of producing sound reproducer cones, consisting insecuring two fabric sheets together at the centers of the sheets,stretching same between two spaced 'frames by first securing andstretching one sheet taut and fiat while the other remains loose, thenstretching and securing the second sheet and gradually increasing thetension thereby drawing the first sheet into a shallow cone, and finallystretching both cones by applying pressure between said frames.

13. The method of producing sound, reproducer cones, consisting insecuring two fabric sheets, one larger than the other, together at thecenters of the sheets, stretching same between two spaced frames byfirst securing and stretching the smaller sheet taut and flat while thelarger sheet remains loose, then stretching and securing the secondsheet forming same into a deep cone, gradually taking up said sheetstep-by-step around its frame thereby increasing its tension, reducingthe depth of the cone and drawing the first sheet into a shallow cone,finally stretching both cones by applying pressure between said frames,and then applying a waterproofing solution to said cones.

This specification signed at New York city, in the county and State ofNew York, this 10th day of April, 1929.

EDW'ARD FREUND.

